An exhaust gas sensor may be positioned in an exhaust system of a vehicle to detect an air/fuel ratio of exhaust gas exhausted from an internal combustion engine of the vehicle. The exhaust gas sensor readings may be used to control operation of the internal combustion engine to propel the vehicle.
Degradation of an exhaust gas sensor may cause engine control degradation that may result in increased emissions and/or reduced vehicle drivability. In particular, an exhaust gas sensor may exhibit six discrete types of degradation behavior. The degradation behavior types may be categorized as asymmetric type degradation (e.g., rich-to-lean asymmetric delay, lean-to-rich asymmetric delay, etc.) that affects only lean-to-rich or rich-to-lean exhaust gas sensor response rates, or symmetric type degradation (e.g., symmetric delay) that affects both lean-to-rich and rich-to-lean exhaust gas sensor response rates. The delay type degradation behaviors may be associated with the initial reaction of the exhaust gas sensor to a change in exhaust gas composition.
Previous approaches to monitoring exhaust gas sensor degradation, particularly identifying one or more of the six degradation behaviors, have relied on intrusive data collection. That is, an engine may be purposely operated with one or more rich-to-lean or lean-to-rich transitions to monitor exhaust gas sensor response. Attempts have also been made to monitor exhaust gas sensor degradation during a deceleration fuel shut-off (DFSO) transition to perform an unobtrusive diagnostic operation. However, vapor purge operation may negatively affect exhaust gas degradation monitoring during DFSO. For example, if vapor purging operation is implemented in the engine during sensor monitoring, the exhaust gas sensor may be incorrectly diagnosed. For instance, an indication of sensor degradation may be provided when the sensor is properly functioning or vice-versa. Other attempts have been made to inhibit this incorrect diagnosis simply by inhibiting sensor diagnostics when fuel vapor purge operation is occurring. However, this may limit window for sensor diagnostics and as a result decrease the number diagnostic operations performed. Consequently, combustion operation may be degraded when a degraded sensor is not diagnosed in a desired time period.
The Inventors herein have recognized the above issues and identified a non-intrusive approach for exhaust gas sensor diagnostics that may be performed during vapor purge operation. In one embodiment, a method of monitoring an exhaust gas sensor coupled in an engine exhaust in an engine is provided. The method includes adjusting engine operation responsive to exhaust gas sensor degradation, the degradation identified during deceleration fuel shut-off (DFSO) and compensated based on whether vapor purge operation is occurring in the engine during DFSO.
Adjusting engine operation based exhaust gas sensor degradation and compensating the degradation based on vapor purge operation decreases the likelihood of sensor misdiagnosis, thereby increasing the confidence of the sensor diagnostic method. Additionally, correcting sensor diagnostics for purge operation enables sensor diagnostics to be performed over a wider range of engine operating conditions. As a result, periods of sensor malfunction without degradation identification are reduced. Additionally, by determining degradation of an exhaust gas sensor using a non-intrusive approach with data collected during DFSO, exhaust gas sensor degradation monitoring may be performed in a simple manner.
In one example, the exhaust gas sensor degradation may be based on a line length and a time delay of a set of exhaust gas sensor response samples collected during DFSO. The exhaust gas sensor time delay and line length may provide a robust signal that has less noise and higher fidelity than previous approaches. In doing so, the accuracy of the sensor degradation determination may be improved.
In a further example, adjusting engine operation responsive to exhaust gas sensor degradation may include adjusting an amount of fuel injection and/or timing of fuel injection in response to exhaust gas sensor degradation. In this way, the combustion operation may be adjusted to account for sensor malfunction to improve combustion operation and decrease emissions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Additionally, the above issues have been recognized by the inventors herein, and are not admitted to be known.